Deep Space Navigation

Background

Space navigation is still largely performed on the ground. Most commonly, tracking stations take measurements of the spacecraft and process the data. Ground-based navigation is very accurate and has been used to successfully navigate spacecraft. But it is very expensive, not robust to loss of contact, space segment degradations and other factors.

There have been some missions that have demonstrated autonomous navigation in flight. This includes NASA's DS-1 mission that performed orbit determination using optical triangulation. Reduced State Encounter Navigation (RSEN), using optical images as the sole data type, was used on DS-1 to track comet Borrelly for 2 hours through closest approach. RSEN is initialized using the last ground or onboard estimate of spacecraft state relative to the target just before commencement of the final approach phase. RSEN was also in the Stardust mission during comet Wild-2 flyby, and in the Deep Impact mission to navigate the impactor to hit an illuminated area on the comet Tempel 1 and by the flyby spacecraft to track the impact site.

The Japanese asteroid return mission Hayabusa employed wide-angle cameras for onboard navigation, in conjunction with Light radio Detecting and Ranging (LIDAR) for measurement of altitude with respect to the asteroid Itokawa. A target marker was dropped to act as a navigation aid by posing as an artificial landmark on the surface. European Space Agency's Small Missions for Advanced Research in Technology (SMART-1) mission employed the Advanced Moon Imaging Experiment (AMIE) camera for Onboard Autonomous Navigation (OBAN). The OBAN framework is also being used for designing a vision based autonomous navigation system for future manned Mars exploration missions

Phase I SBIR: Optical Navigation System

This SBIR Phase I research is for a flexible navigation system for deep space operations that does not require GPS measurements. The navigation solution is computed using an Unscented Kalman Filter that can accept any combination of range, range-rate, planet chordwidth, and angle measurements using any celestial object. The UKF employs a full nonlinear dynamical model of the orbit including gravity models and disturbance models. The filter will estimate both states and parameters. The sensor employs three methods for getting position information. The first is from chordwidth measurements of the Sun. This camera always looks at the solar disk. The second camera measures the angles between planets in the solar system. The center measures the angle from planetary centroid to planetary centroid. The third sensor measures angles between stars and the Sun vector. Each snapshot from the system provides a 3-axis measurement.

The navigation system is being developed by Princeton Satellite Systems and the sensor is being developed by Professor Michael Littman of Princeton University. A complete navigation simulation and preliminary sensor mechanical drawings will be delivered at the end of Phase I.

See the movie of a deep space trajectory at Deep Space Simulation

Phase II SBIR: Optical Navigation System

In Phase II the flight software and prototype optical sensor are being built. Several additions have been made to the system. The sensor now does attitude determination using either of the two cameras. The software also performs batch orbit determination in background which is used to reset the recursive filter. The attitude determination software also uses the Unscented Kalman Filter with its own nonlinear measurement model. The system has a built in MEMS Inertial Measurement Unit (IMU) which provides that attitude dynamics based for attitude determination and measurements of non-gravitational accelerations.

The optical navigation system is an autonomous, flexible spacecraft navigation system for deep space and planetary orbit operations. The primary sensor includes two telescopes. Each telescope has a gimbal mount with two degrees of rotational freedom. The gimbal angles can be measured up to very high resolution. Each telescope can be zoomed using linear actuators with nano-meter precision. The design allows for simultaneous optical measurements of multiple celestial objects. Measurements will include solar and planetary chord widths, landmarks, and angles between planets, stars and the sun vector, as shown in the figure below on the left hand side.

The navigation solution is computed using an Unscented Kalman Filter (UKF) that can accept any combination of range, range-rate, planet chord width, and angle measurements using any celestial object. The UKF employs a full nonlinear dynamical model of the orbit including gravity models and disturbance models. Attitude estimation is also performed using a UKF filter for integrated optical measurements and accelerations measurements from an on board IMU.

The instrument is designed with a 50 mm aperture and a 50 mm focal length without zoom. The scopes use zoom lenses to provide a maximum magnification of 15.9. It can be used either in a first focus "camera" mode, or, using an objective lens, in a second focus "projection telescope" mode. The sensor can operate in a higher precision mode in which the camera sequentially centers on one target and then rotates and centers on a second with a high precision relative angle measurement. Changes in optical instrument dimensions and sensor accuracies have a major impact on the navigation accuracy, which can be tailored to suit specific applications.

The 6U CompactPCI single-board computer that employs the PowerPC RAD750 microprocessor, the radiation hardened version of the IBM PowerPC 750 microprocessor is used. The 6U board has built-in SpaceWire for both internal and external sensor interfacing. Complementary metal-oxide-semiconductor (CMOS) active-pixel sensors, with a global shutter, will be incorporated. The sensor includes an IMU. The accelerometers on the IMU provide accurate measurements of disturbance accelerations and the gyros provide an attitude dynamics base for attitude determination.

Not only does the proposed instrument allow for snapshot operation to determine 3-axis position and attitude, it also can be used in continuous operation. The navigation filter can accept simultaneous or sequential measurements. The optical sensor design reflects a compromise of competing needs including size, weight, and performance. Robust operation and graceful degradation is planned through complementary optical, mechanical, electronic, and networking components. If one telescope fails, the mission can be completed using the other alone. Each telescope has a separate processor connected in a redundant network making the sensor fully single fault tolerant. All components of the flight-ready version will be radiation-hard and single-event-upset-and-latch-up immune.

The laboratory prototype and a lunar image are shown below.

The completed prototype on its astronomical tripod is shown below.

The navigation software API can be found here Navigation Software API.